Playing around with functional iterables in ES6.

iterables.es6

function *range(start, end, skip) {
  if (typeof skip === 'undefined') {
    skip = 1;
  }
  
  if (typeof end === 'undefined') {
    end = start;
    start = 0;
  }
  
  for (let i = start; i < end; i += skip) {
    yield i;
  }
}

function iterTools(iterable) {
  return {
    map: map,
    reduce: reduce,
    chunk: chunk,
    every: every,
    some: some
  };
  
  function *map(fn) {
    for (let i of iterable) {
      yield fn(i);
    }
  }
  
  function reduce(fn, initializer) {
    if (typeof initializer === 'undefined') {
      initializer = 0;
    }
    
    let c;
    let p = initializer;
    for (c of iterable) {
      p = fn(p, c);
    }
    
    return p;
  }
  
  function *chunk(size) {
    let chunk = [];
    
    for (let item of iterable) {
      chunk.push(item);
      
      if (!(chunk.length < size)) {
        yield chunk;
        chunk = [];
      }
    }
    
    if (chunk.length) {
      yield chunk;
    }
  }
  
  function every(fn) {
    for (let i of iterable) {
      if (!fn(i)) {
        return false;
      }
    }
    
    return true;
  }
  
  function some(fn) {
    for (let i of iterable) {
      if (fn(i)) {
        return true;
      }
    }
    
    return false;
  }
}

var isEven = (x) => Math.floor(x / 2) === x / 2;
var square = (x) => x * x;
var sum = (x, y) => x + y;

for (let i of range(2)) {
  console.log(i);
}

for (let i of range(2, 4)) {
  console.log(i);
}

for (let i of range(4, 10, 2)) {
  console.log(i);
}

console.log(iterTools([2, 4, 6]).every(isEven));
console.log(iterTools([2, 4, 6, 1]).every(isEven));
console.log(iterTools([2, 4, 6]).some(isEven));
console.log(iterTools([2, 4, 6, 1]).some(isEven));

for (let i of iterTools(range(0, 16, 7)).map(square)) {
  console.log(i);
}

console.log(iterTools(range(4)).reduce(sum));

for (let i of iterTools([1, 2, 3, 4, 5, 6]).chunk(3)) {
  console.log(i);
}